I think it's both true and false.

I think if you do what you love, you will find a way to monetize it... you will ENJOY working your posterior off at it... you will find the money to invest in it... etc, etc, etc.

They say that success comes from either one of three sources:

Inspiration.
Desperation.
And perspiration.

Doing what you love won't make you rich. It just makes the process of getting there easier or at least more livable.